Popular Science Monthly/Volume 11/September 1877/The Observatories of Italy
By Professor G. RAYET.
IN the course of my journey in Italy, I visited successively the observatories of Palermo, Naples, Rome (that of the Roman College as well as that of the Capitol), Florence, Bologna, Modena, Padua, Milan, and Turin, remaining some time at each. There are thus no less than ten observatories in Italy, three times as many as in France; and from the proceedings of the Congress of Astronomers at Palermo it appears that it is the intention of the Government to maintain all of them, each one being devoted, however, to a different branch, so as to fulfill the various needs of astronomical science, now become so complex.
Of these observatories, only that of Naples has a considerable number of assistants, and in no one is the work done under rigid regulations; each astronomer devotes himself, according to his predilections, to a special subject; emulation and the desire to make a name in science produce a continuity of effort the result of which has in the last few years been manifest in various brilliant discoveries. To show this, it will be sufficient to describe briefly the situation of each observatory, and the work upon which it is at present engaged.
The Observatory of Palermo: Director, M. Cacciatore; Astronomer, M. Tacchini.—This observatory contains two important instruments: a meridian-circle, constructed in 1857 by Pistor and Martins (of Berlin), whose telescope has an aperture of 126 millimetres (4.98 inches), and an equatorial by Merz (of Munich), of 24 centimetres (9.45 inches) aperture, which, though built in 1857 was not mounted until 1865. The meridian-circle was employed in 1870 to determine the difference of longitude between Naples and Palermo, this last point being the fundamental station in the new topographical map of Sicily, and it is daily employed in observations of the sun and the principal stars. The most important work, however, of the observatory of Palermo, which is specially undertaken by M. Tacchini, is the daily study of the solar protuberances.
Since the total solar eclipse of 1868, a great number of astronomers have devoted themselves to the daily observations of these protuberances, in order to study their distribution on the solar circumference, and their relations with solar spots. Among these astronomers are Lockyer, Secchi, Rayet, Respighi, Tacchini, and Young, but it is in Italy that these researches are most vigorously prosecuted, and, in order to avoid the interruptions in a series which cloudy days may occasion, the observatories of Palermo, Rome, and Padua, prosecute these observations in common.
Every day, when the weather will permit, M. Tacchini makes a drawing of the protuberances surrounding the border of the sun and of the spots and faculæ which are upon its surface. These drawings, as well as those made at Rome and Padua, are subsequently published in the "Memoirs of the Society of Italian Spectroscopists," whose publications, begun in 1872, form already four large quarto volumes.
For this work, M. Tacchini makes use of the large equatorial of the observatory, and a direct-vision spectroscope made by Tauber, of Leipsic, which has two series of five prisms. These prisms are of rare excellence, for, in spite of their number, the spectral lines suffer no distortion. The spectroscope can be rotated on its axis so that it can be placed tangentially on any portion of the sun's circumference. Among the interesting historical instruments of the observatory is the altitude and azimuth circle made by Ramsden in 1788-'89, which served Piazzi in the preparation of his great catalogue of stars.
The Observatory of Naples: Director M. de Gasparis; Astronomers, MM. Fergola, Brioschi, and Nobile.—The observatory of Naples is the most important of those of Italy, in its equipment and its personal establishment.
It was founded in 1812 by Murat, and it is built in agreement with modern ideas. It contains numerous instruments which are maintained in perfect order by the care of an instrument-maker attached to the observatory. In the west meridian room are a transit-instrument by Reichenbach (aperture 117 millimetres 4.61 inches), and a meridian-circle by the same artist (aperture 108 millimetres 4.25 inches). These are still in use, and by means of them M. Fergola has lately determined the differences of longitude of Naples with Rome and Palermo. The east meridian room contains a meridian-circle by Repsold, which has just been mounted, and which is one of the best instruments of this class made by this celebrated artist. The telescope has an aperture of 163 millimetres (6.42 inches), and a focal distance of two metres (8.74 inches). It has a single graduated circle, one metre (39.37 inches) in diameter, and four microscopes.
It is with this instrument that M. Fergola is observing the zone of stars which the observatory of Naples has undertaken for the German Astronomical Society. Besides the three meridian-instruments the observatory of Naples has in active use two equatorials, and is soon to obtain a third of larger dimensions. The first of these instruments was constructed in 1811 by Reichenbach and Utschneider, and has 83 millimetres (3.27 inches) aperture. It is with this small instrument that M. de Gasparis discovered nine asteroids, Ilygea, Parthenope, Egeria, Eunornia, Psyche, Massalia, Themis, Ansonia, and Beatrix. The second equatorial was made by Merz, of Munich, and has 134 millimetres (5.28 inches) aperture, and 2.06 metres (81.10 inches) focal length. The objective is of so perfect a figure that, in spite of its small dimensions, M. Nobile has been able to employ it in the measurement of double stars of Struve's catalogue. (These were discovered by Struve with an objective of 9.62 inches aperture.)
Observatory of the Roman College: Director, Padre Secchi; Astronomer, Padre Ferrari.—The observatory under the direction of Padre Secchi is built upon the top of the cupola of the church of St. Ignatius, near the Corso; but in so solid a way that the stability of the instruments, during the night at least, is quite satisfactory. The principal instrument of the observatory is an equatorial of 7.5 inches aperture, which is one of the chefs-d'oeuvre of Merz. There is still another equatorial, by Cauchoix, of five inches aperture, which is used for the daily observations of solar spots, and also a transit-instrument by Ertel (aperture 92 millimetres 3.62 inches), for time-determinations. The situation of the observatory, in the centre of the city, has forced its illustrious director to devote his efforts to the study of physical astronomy, which in his opinion is too much neglected in government observatories.
To enumerate the magnificent works executed in this branch of astronomy by Padre Secchi would require too much space, but I may mention a new experimental method used by Padre Secchi in his studies of the solar protuberances. For more than a year he has employed in place of the prisms of his spectroscope a diffraction-grating ruled upon speculum metal by Lewis M. Rutherford, Esq., of New York City. This grating has 4,000 lines to the English inch, and gives a spectrum whose definition leaves nothing to be desired. For the study of the solar prominences such a grating appears to me infinitely superior to any combination of prisms.
Observatory of the Capitol: Director, M. Respighi; Assistant, M. Scarpellini.—The second observatory in Rome, that of the Capitol, is under the patronage of the Accademla dei Nuovi Lincei. It is placed upon the summit of the southeast portion of the palace of the Capitol, and it is sufficiently removed from the neighborhood of traveled streets to preserve it from the vibrations caused by carriages, etc. The instruments are undisturbed enough to allow of the most delicate astronomical observations, such as the determination of the nadir-point and the observation of stars by reflection from the surface of quicksilver, at all hours of the day.
The horizon is also entirely free, so that if the situation allowed of a more regular placing of the instruments it might be considered as very favorably situated for the making of observations of precision. M. Respighi is now occupied in observations of solar protuberances, and in meridian observations, which are to serve as a basis for a catalogue of stars. For the first purpose an equatorial by Merz, of four and a half inches aperture, and a direct-vision spectroscope with five prisms, are employed.
A beautiful meridian-circle by Ertel serves M. Respighi for his observations of those fixed stars of the first six magnitudes, which are to be employed by the Italian staff-officers in their geodetic operations. This observatory possesses also a reflex zenith-tube, made by Ertel from designs by M. Respighi himself. It is a sort of transit-instrument, with an aperture 108 millimetres (4.25 inches), provided with an eyepiece which contains three groups of declination-wires. The basin of quicksilver, by means of which the reflected stars are observed, is 21 metres (68.90 feet) below the objective, which thus masks but a small portion of the sky. When the telescope is directed toward the nadir stars very close to the zenith may be observed by the declination-wires during their transit; at the same time and without touching the instrument the nadir may also be observed, so that the zenith-distance of each star depends upon the micrometer-screw alone and is determined with the great accuracy which this kind of observation allows.
Observatory of Florence: Assistant, M. William Tempel.—The old observatory of Florence, formerly presided over by Donati, has been dismantled, and a new and magnificent structure is nearly built at Arcetri, near the house formerly inhabited by Galileo. The old observatory is now used for a meteorological station, under charge of Prof Pitti.
The new observatory possesses: 1. A Fraunhofer equatorial of three inches aperture, suitable for a comet-seeker; and, 2. A large equatorial by Amici, of eleven inches aperture, of excellent quality. Besides this, a small meridian-instrument is mounted in the meridian-room. This room will subsequently contain a meridian-circle of seven inches aperture, and a transit-instrument somewhat smaller. It is proposed to have for this observatory a staff composed of a director and five assistants.
Observatory of Bologna: Director, M. Palagi.—The observatory of the University of Bologna is one of the most ancient in Italy, and, like all the observatories of the past century, it is placed on the top of a high tower, which unfits it for precise observations. In the plan proposed for the reorganization of the Italian observatories, this institution is to devote its labor to observations of physical astronomy. It possesses a meridian-circle, by Ertel, of forty-two lines (3.5 French inches) aperture, mounted in 1851, but now little used, and also a Dollond equatorial of three inches aperture. Its collection of historical instruments is of high interest.
Observatory of Modena: Director, M. Ragona.—Modena is an astronomical city, for in it or near it were born Amici, Secchi, Tacchini, Ferrari, and other Italian astronomers. The Ducal Observatory is, like that of Bologna, in a transition state. It was founded in 1819, by Bianchi, and was provided with the best instruments of that time, but it now will probably become the central meteorological station of the surrounding states. Its meridian-circle is of four inches aperture with three-feet circles, and was made by Fraunhofer and Reichenbach in 1819, but requires some changes to bring it up to modern requirements. Its Amici equatorial has two and one-third inches aperture only, and is thus too small for most astronomical purposes. Its collection of meteorological and magnetic apparatus is, on the contrary, very complete and noteworthy, and has been made, in most cases, upon plans furnished by M. Ragona.
Observatory of Padua: Director, M. Santini; Astronomer, M. Lorenzoni.—This observatory dates from 1774, when this city was placed under the protectorate of Venice, and when this powerful republic attracted the most celebrated professors to its university. It is well situated for observations of precision, as the numerous catalogues of stars published by its celebrated director, now the oldest living astronomer, testify sufficiently. The principal instruments of the observatory are a meridian-circle and an equatorial, both by Starke—the first of 117 millimetres (4.61 inches) aperture and with one-metre (39.37 inches) circles; the second with twelve centimetres (4.74 inches) aperture and two metres (78.74 inches) focal length. There is also a spectroscope by Hoffmann. The two latter instruments are used by Lorenzoni for daily observations of the solar protuberances. The meridian-circle is employed in observations of the sun, planets, and the principal stars, and can even observe stars down to the tenth magnitude by means of a peculiar device for bright wires.
Observatory of Milan: Director, M. Schiaparelli; Astronomer, M. Celoria.—The Milan Observatory is one of the most ancient of Italy, its foundation in the Brera Palace having been established in 1760. Among its directors have been the celebrated astronomers Boscovich, Oriani, Cesaris, and Carlini. The Ephemeris of Milan has long been distinguished for its accuracy, and for the memoirs published in connection with it by Oriani, Cesaris, and Schiaparelli. The observatory contains two halls, one for the equatorial and one for the meridian-circle. The equatorial, by Merz, was mounted in February, 1875. It has an aperture of 218 millimetres (8.58 inches), and a focal length of 3.20 metres (125.99 inches), and its objective is of such an excellence that a magnifying power of 700 diameters is habitually used. It is to be devoted to a reobservation of Struve's double stars. The meridian circle is by Starke, and has an aperture of four inches and a focal length of five feet.
Observatory of Turin: Director, M. Dorna; Assistant, M. Charrier.—The present observatory of Turin was constructed in 1820, and until 1864 it was under the direction of the illustrious Plana; since that time it has formed part of the university, and is under the charge of the Professor of Astronomy. Its instruments are: 1. A meridian-circle by Reichenbach, with a circle one metre (39.37 inches) in diameter, and a telescope by Fraunhofer, twelve centimetres (4.74 inches) in diameter. This excellent instrument is used for observations of the sun and stars for the determination of the time, which is given to the city by means of a time-ball. 2. A comet-seeker of twelve centimetres (4.74 inches) aperture and eighty-two centimetres (32.28 inches) focal length, mounted in a small dome. 3. A repeating circle, by Ertel, used for purposes of instruction. 4. An equatorial of 117 millimetres (4.61 niches) aperture and 1.82 metres (71.65 inches) focus, which will be used by Dr. Charrier for spectroscopic observations of the solar protuberances. A larger equatorial is soon to replace this.
In terminating these short notes I must formulate in a few words the reflections which my visit to so many institutions has suggested to me. The simple enumeration of the instruments would ill suffice to judge of their importance. It is not sufficient that an observatory should be provided with numerous or powerful instruments: it is further necessary that these instruments should be at, the service of accomplished astronomers earnest in the pursuit of their studies, and having no other desire than to achieve a name in science. In all these respects the observatories of Italy leave the most satisfactory impression upon the visitor. Thanks to this universal ardor, no moment is lost; and Italian astronomy, which for a time languished, is reconquering with marvelous rapidity the rank which the labors of Galileo assured to it at the beginning of the seventeenth century.